Discharge tube with glow cathode



Aug. 30, 1932. HQLST 1,875,002

DISCHARGE TUBE WITH GLOW CATHODE Filed March 17, 1924 l'l'l'l l'l ifl ll @AZZM/W 5 L7; 747% Patented Aug. 30, 1932 UNITED STATES,

PATENT OFFICE GILLES HOLST, OF EINDHOVEN, NETHERLANDS, ASSIGNOR TONAAMLOOZE VENNOOT- SCHAP PHILIPS GLOEILAMPENFABRIEKE'N, 0F EINDHOVEN,NETHERLANDS DISCHARGE TUBE-WITH GLOW CATHODE Applicationifiled March 17,1924, Serial No. 699,906, and in the Netherlands March 29, 1923.

This invention relates to improvements in incandescent cathode-dischargetubes, and more particularly to the arrangement and the construction ofthe incandescent cathode as well asin the way of heating the same.

The invention has special advantages when applied to electric dischargetubes having threeelectrodes and used as receiving tubes for detectorsin wireless telegraphy, wireless telephony and similar purposes.

In this kind of discharge tubes particularly when used byamateurs thedisadvantage has made itself felt, in that a batteryof direct current isnecessary for heating the oathode and the repeated recharging of saidbattery is troublesome and expensive. Heating the filament withalternating current has the disadvantage that in consequence of thechanges of temperature of the incandescent cathode and the changes inintensity of the magnetic field produced around the latter additionalsounds are observed in the telephone.

The invention has for its purpose to enable the use of alternatingcurrent whilst avoiding the aforesaid detrimental efiects.

It is known to heat the incandescent cathode of electric discharge tubesby conduction or radiation of heatwith the aid of heating units disposedWithin the tube. It has also been suggested to provide incandescentcathodes, the surface of WhlCll'GOIlDLlIlS material which yields anemission of electrons that is sufiicient for the operation of the tubeat a materially lower temperature than that of an incandescent tungstenfilament.

, According to the invention the discharge tube comprises such a cathodeand in addition one or more heating units which conduct an electriccurrent and are to be heated by said current, said heating units beinglocally in direct contact with the cathode but for a considerable partclear of it, said cathode being heated essentially by the conduction ofthe heat developed in the heating units to the cathode across the placeof contact.

This method has the advantage that the heating current does not flowthrough the cathode itself, and alternating current can be usedforheating the heating units without the aforesaid disadvantages.

It is of course, obvious that it is not possible to heat the cathode byheat conduction to such a temperature as would be necessary for asufiiciently intensive emission of electrons of tungsten. It is moreoverunneces sary if the surface of the vcathode has applied thereto materialwhich at a low temperature easily emits electrons. It is also obviousthat the cathode may be constructed entirely of the said material. It isessential only that the surface of the cathode contains material havingthe aforesaid favorable property. Such'materials which at acomparatively low temperature emit electrons to a marked extent andneither fuse at this temperature nor obtain an inadmissably high tensionof vapour are known. As an example the oxides of the alkaline earthmetals, for example barium oxide may be mentioned.

It mustbe remarked that the heating of the cathode which according tothe invention principally takes place by heat conduction is partlyeffected in another way, that is to say, by radiation of heat.

According to the invention a particularly simple construction isobtained if the heating units also supports the cathode.

Furthermore it is advantageous to make the cathode principally of ametal that conducts beat well, and the heating units are preferablyconstructed of material such for example as chrome iron,nickel-chromium, or similar material having a high resistance.

The choice of a material having a high specific resistance isadvantageous because the heating wires if they also support the cathode,must for this reason have a relatively large diameter.

When applying the invention to a discharge tube in which the electrodesare arranged concentrically, the cathode may at each end he carried by aheating wire.

Furthermore it is advisable to supply the heating units and theincandescent cathode with separate leading-in wires, so that theincandescent current circuits are quite independent of the cathode gridcircuit and the cathode anode circuit.

For heating the heating units, a transformer may be used, the primarywinding of which is capable of being connected to a voltage ofalternating current of the usual value for example to the lightingsysteln of a town.

Obviously it is detrimental if the cathode leads current from oneheating unit to the other. In order to prevent this, one may either heatthe heating units in entirely separated circuits for example by usingseparate secondary coils or 'care may be taken that the cathode makescontact with those pointsof the heating units whichhave practically thesame potential.

' cient. -More0ver all the points of the cathode I as the invention.

In the latter case the leadin wires for the heating unitsinay also bebranched-within the lamp, so that less leading-in wires need be sealedin and one secondary Winding 1s sufiihavethe same potential,so that itis possible to maintain the advantages of the known equiment.

"Figure 2 is a. side view of the tube shown in Figure 1.

Figure 3 represents in perspectivethe stem of tube shown in Figure 1;said stem having fixed thereto the cathode.

Figure 4' shows a different construction of an electron emitting cathodewith heating units.

The tube shown on the drawing comprises an exhausted vessel 1 of glassfor example having vhermetically sealed thereto a glass stem 2,leading-in wires for the various parts of the discharge tube being.hermetically sealed in the clamped portion of the stem.

' VVithin' the envelope 1 are en'closed'an anode 3, a grid andanelectron emitting cathode 5. Theanode 8 consists of a cylindricall ybent plate. which maybe of some suitable electrode material such forexample as, nickel, and 'is carried atthe two ends by supporting wires 6and 7, the latter of which also serves as a leading-in wire.

-: The grid 4. consists of 'a helically' bent wire 7 for example ofnickelg n olybdenum, tungsten, or other suitable material, and iscarried at the two ends by supporting wires 8 and 9, the latterofwhichalso serves as leading-in wire.

In the agrisof the electrodes 3 and 4, which front elevation of adischarge I The other electrodes are omitted in th s figure.

are arranged concentrically in relationto" each other is found thecathode 5 which is preferably of material that conducts heat Well, forexample of copper and Wliiclris coated at its surface with materialthateasily emits electrons at a comparatively low' teni perature such forexample as an alkaline earth metal oxide.

The cathode is carried at its end by two wireloops 11 and- 12 (see alsoFigure 3% which serve as heating wires and preferably consist, ofmaterial having a high resistance such for example as chrome-iron ornickelchromium. Theloop I1 is carried'at its ends by supporting wires 13and 1 1, the lattero'f which serves as a leadingin wire, whereas theloop 12 is carried by supporting wires 15' and wires areinconductiveconnection by wires the wire'15fbeing used asia leadingi 'iWithinthe tube the ends of the heating 17 and18-s0 that for i'eeding thecurrent-to V the said heating wires it is only-necessary that p twowires are sealed in-the clamped portion of the stem.

' The drawing shows that thecathode 5' makes contact with thosepointsof-the heat s ing wires'that practically have the same' potential' 'sothat no current fiows" through thecathode '5. In addition the cathode 5ispro vided with'a' separate leading-in wire 10,

which has the aforementioned advantages.

a A high vacuum maybe provided in known 1 manner within-thebulb landfor. this pur pose'the. glass walland' the-surface of the electrodes mayin knownmanner be deprived of the occluded gases; F or obtaining a threeelectrode tube of these-called soft typeg-a sorted to.

-By reference to Figure 1--the 'circuitarrangenient oi? the' dischargetube shown on the drawing will be briefiydescribed For heating theheatingwires 11' and 12 a transformer 20, 19 is provideditheprimarygaseous filling of'low pressure may; b re winding 20 of which maybeconnected by means of a switch 21 to an alternating current circuit ofthe usual voltagerlorexample to.

the lightingsystem of a town; The transformer whi'ch need transmit onlya very: low

power maybe of simple construction. In'the anode circuit are. interposeda battery 23 and a telephone 25," whereas the grid circuit are provided:airegulating con;

denser 26iand parallel thereto a regulating inductance 24, the latter ofwhich: maybe used for intercepting variations ofvoltage;

i In a. construction shown in Figure 4; a

cathode-3O is carried by heating coils 31 and 82, a thin layer ofinsulating material33: be ing applied between thecathode and the wire 1.In an electron discharge tube, cathode unit including athermallyiconductive.catlh.

ode member adapted to emit electrons when heated, a plurality ofindependent electric heaters each in thermally conductive relation tosaid member, a plurality of pairs of branch conductors, the branchconductors in each of said pairs being respectively connected at theiradjacent ends to one of said heaters to supply current thereto, and twomain conductors each connected respectively to the free end of onebranch conductor in each of said pairs whereby currents alike in phaseare delivered tosaid heaters simultaneously, and whereby said cathodemember is established in relation to said heaters at equi-potentialpoints in said heater and branch conductor circuits.

7 '2. In an electron discharge tube, an elongated thermally andelectrically conductive cathode adapted to emit electrons when heated, agrid and an anode, a plurality of electric heaters thermally andconductively connected to said cathode, and conductors to supplycurrents to said heaters, said cathode being electrically connected toequipotential points of said heaters.

3. In an electron discharge tube, an electrically and thermallyconductive cathode of substantial heat capacity adapted to emitelectrons when heated, a grid and an anode, a conductor includingbranches to supply heating current, an electric heater in each of saidbranches, said cathode being connected in thermally and electricallyconductive rela tion to said heaters at equipotential points on saidbranches.

4. A cathode comprising an electron-emitting member and a plurality ofheating units, each of the heating units being adapted to conduct anelectric current and to be heated by said current, the electron-emittingmember contacting with each of the heating units at only one point, theelectron-emitting member being supported by the heating units at thosepoints at which the electron-emitting member is in contact with theheating units.

5. A cathode comprising an electron-emitting member and a plurality ofheating units, each of the heating units being adapted to conduct anelectric current and to be heated by said current, the electron-emittingmember contacting with each of the heating units at only one point, theelectron-emitting member being supported by the heating units.

6. A cathode comprising an electron-emitting member and a plurality ofheating units,

each of the heating units being adapted to conduct an electric currentand to be heated by said current, the electron-emitting membercontacting with each of the heating units at only one point, theelectron-emitting member contacting with those points of the heatingunits which have substantially the same potential. V

7 In an electron discharge tube an elongated thermally conductivecathode adapted to emit electrons when heated, a grid, an anode, and aplurality of electric heaters in thermally conductive relation to saidcathode, said heaters being spaced apart and surrounding oppo'site endsof said cathode.

8. An electron discharge tube comprising an anode, a grid, and anelongated thermally conductive cathode capable when heated of emittingelectrons from its middle portion, and a pair of electric heaterspositioned adj acent the end portions only of said cathode and spacedapart sufficiently to permit an unobstructed emission of electrons fromthe outer surface of the middle portion of said cathode, each of saidheaters comprising a wire loop outside of and in thermally conductiverelation to the cathode end adjacent said loop.

In testimony whereof I aflix my signature, at the city of Eindhoven,this 25th February DR. GILLES HOLST.

